The laser efficiency and service life have been measured for two different dye-doped solid media: a modified PMMA and an optical epoxy. The samples were longitudinally pumped using the output of either a Q-switched, frequency-doubled YAG laser (532 nm; (tau) _p approximately equals 8 ns) or a flashlamp- pumped dye laser (490 nm; (tau) _p approximately equals 1.5 microsecond(s) ). The much longer pump pulse of the dye laser can lead to significant differences in performance in such areas as optical damage, dye photobleaching, thermo-optical distortion of the gain medium, and the relative importance of triplet absorption. The impact of pump pulse duration on laser performance parameters will be discussed.

Presented here are experimental results for a high-energy solid-state dye laser with different laser resistant polymer active elements impregnated with pyrromethene and xanthene dyes. It was pumped by a unique frequency doubled Medlite^TM IV Nd:YAG laser with pulse energies up to 660 mJ, pulse width 5 - 7 ns and pulse repetition rates up to 10 Hz developed by Continuum Biomedical. A dye laser output energy greater than or equal to 525 mJ in broad band operation mode and slope efficiency over 80% were demonstrated at pump fluences up to 3 J/cm$2). No laser-induced damage of the modified polymer elements was detected up to these levels of fluence. A stable output for more than 150,000 pulses at 585 nm, for a fixed area of the polymer element, at a pump fluence of 1.3 J/cm² has been achieved.

The life of high power short pulse flashlamps for dye lasers has been examined and a key degradation process identified. Three main effects have been identified and characterized. These are an initial steep drop in optical output followed by a slow decline in output with continuous running and an output recovery after a rest period. Mass spectroscopy has shown that there is a substantial build-up of oxygen in the flashlamp during the first few pulses. The oxygen is believed to be a result of the break-up of the quartz wall. Using this simple process of wall erosion the three effects above have been explained. This has led to a new model to predict the life of short pulse, high power flashlamps where operational lifetime is dominated by wall erosion rather than thermal stress.

Local intensity fluctuations in a large aperture dye laser have been analyzed. We have studied the influence of solvent viscosity in the amplitude of these fluctuations. This experimental result provide a clear evidence of the role played by the molecular orientation in the spatio-temporal laser dynamics. The dependence of the average spectra of these fluctuations on the active laser medium length has been studied. The mean frequency of the spectra change with the active laser medium length.

The first demonstration of a flashlamp pumped zig-zag liquid dye laser is presented. Repetitively pulsed measurements with liquid Pyrromethene-567 demonstrated 230 mJ per pulse at 1 Hz. This design will be used to test solid state plastic host dyes.

The DERA has been active in the research and development of dye laser technology for in excess of fifteen years. During this period emphasis has been placed on the investigation of techniques that will produce a compact, reliable, safe and efficient flashlamp pumped liquid phase dye laser. Recent studies have involved solid state dye lasers including dye doped polymers.

The photophysical and lasing properties of pyrromethene dyes in epoxy resins have been investigated. These resins show a relatively high damage threshold, as well as good lasing efficiency. Fluorescence properties for PM dyes in epoxy hosts, including quantum efficiencies and lifetimes, have been obtained.

Synchronously pumped optical parametric oscillators (OPOs) offer great promise for the generation of high average power radiation in the mid-infrared waveband. In this report, we assess the potential of using a silver gallium sulphide (AgGaS₂) OPO to achieve such high powers. A number of different OPO cavity configurations have been designed and tested to optimize the conversion efficiency. The pump laser (Nd:YAG) operates at 1.064 micrometer and is both mode-locked and Q-switched. The Q-switch repetition rate is variable between 0.5 and 2 kHz and the maximum mean power available is 8.5 W. Both linear and ring cavities have been tested and the most efficient design produced separate high quality signal and idler beams of average power 1.45 W (1.44 micrometers) and 620 mW (4.06 micrometers) at a pulse repetition rate of 2 kHz. It is believed that these near and mid-infrared powers represent the highest to date with a AgGaS₂ OPO.

BBO is a popular nonlinear optical crystal typically used for frequency conversion. Recently, BBO was also used as electro- optic Q-Switch material. BBO was chosen as a good candidate material for use as an E-O Q-Switch for Er:Glass lasers because of its low insertion losses at 1.54 micrometer and high laser damage threshold (5GW/cm², 10 ns). Traditional materials such as KD*P or LiNbO₃ exhibit high insertion losses and/or low damage thresholds at 1.54 micrometer. As an added benefit, BBO does not exhibit a piezoelectric effect. All of these advantages make BBO an attractive Er:Glass E/O Q- switch for high peak and high average power applications.

Three micrometer erbium lasers can be widely used in medical applications due to water absorption maximum at 3 micrometers. This allows cleaner cuts with smaller destruction of adjacent tissues. A power scaling of laser radiation in this wavelength range with maintaining good beam quality is very important to reach good surgically results. However, many difficulties exist to scale the output power of 3 micrometer erbium lasers. One of them results from thermal lensing in the active materials. To solve this problem, we have realized for the first time an Er:Cr:YSGG laser in a MOPA arrangement incorporating an SBS-cell as phase-conjugating mirror, where also a resonant reflector and a FTIR-shutter as Q-switch were used in the master oscillator. An optical isolator between the master oscillator and the power amplifier at 3 micrometer wavelength was constructed by using a self-made (lambda) /4- plate and a polarizer based on silicon plates technology which function also as the outcoupling device for the phase conjugated beam. The phase-conjugating properties of the output beam were demonstrated by observing the profiles of both input and output beams. An SBS reflectivity of more than 40% and an SBS threshold of below 200 kW were obtained in the CS₂ SBS-liquid. Our results demonstrate that SBS phase conjugation can be also applied for MOPAs with high beam quality of 3 micrometer radiation.

We report the gain measurement of a laser diode pumped Tm:YAG laser by using a cavity loss method. The maximum gain and the saturation parameter of a single-longitudinal-mode Tm:YAG laser were determined to be 0.04 cm^-1 and 13 kW/cm², respectively, were obtained in a single- longitudinal-mode.

Y²⁺ (4d¹ configuration) ion is proposed to be a new laser active optical center. As an example Y²⁺ in CaF₂ crystals demonstrates broad luminescence band with peak at 1146 nm and halfwidth of 2155 cm^-1 at room temperature when excited with 532 nm light. It was observed that Y²⁺ centers in CaF₂ are stable under excitation with 532 nm radiation with pumping power density of 233 MW/cm² from flash-lamp pumped Q-switched Nd³⁺:YAG laser. Optical gain has been measured in CaF₂:Y²⁺ amplifier at 1150 nm wavelength. It is concluded that Y²⁺ doped crystals seems to be promising materials for tunable solid-state lasers.

We report 0.95 kW average output power from a single cw-diode pumped Yb:YAG power oscillator. The 3-mm diameter solid-state laser rod is side pumped by three sets of cw diode arrays each of which has an electrical-to-optical efficiency of up to 50%. Our phase-conjugate master oscillator, power-amp architecture will incorporate this pump cavity as one of the power amplifiers for multi-kW average power, good beam quality laser applications.

Until now active or passive Q-switching have been used to achieve highly energetic laser pulses. Both these pulsing techniques have advantages as well as drawbacks. Passive Q- switching is extremely simple and need no electronic driving, but the emitted pulse has a large time jitter (100 ns to 1 ms) between the emitted pulses, which is detrimental in many applications. Active Q-switching on the other hand require advanced high voltage drive electronics which consume a substantial amount of electrical power, but the emitted pulse train is normally clean and well-behaved. In this paper we propose and demonstrate a novel Q-switched diode-pumped solid- state laser design, which combines the advantages of active and passive Q-switching, resulting in low time jitter as well as simple drive electronics with low power consumption. The plane-plane diode pumped laser consisted of a 0.5 mm long 3% Nd³⁺:YVO₄ crystal acting as the gain medium, with the first mirror directly coated on the input face. The laser chip was followed by the active modulator, a 2 mm long z-cut LiNbO₃ crystal, which in turn was followed by the saturable absorber, a 0.6 mm thick Cr⁴⁺:YAG crystal, and the output mirror. All elements were optically bonded together and the total cavity length including mirrors was 3.5 mm. The monolithic laser has a low jitter, here limited by our driving electronics to 85 ps, at a switching voltage of 300 V, compared to the V_(pi ) of 5.2 kV. The pulse length is only 3 ns when the laser operates in combined Q-switched mode and 12 ns when passively Q-switched. In addition, multiple pulses caused by the active modulator is suppressed by the saturable absorber.

We present the energy, propagation, and thermal modeling for a diode-pumped solid-state laser called Mercury being designed and built at LLNL using Yb:S-FAP [i.e., Yb³⁺-doped Sr₅(PO₄)₃F crystals] for the gain medium. This laser is intended to produce 100 J pulses at 1 to 10 ns at 10 Hz with an electrical efficiency of approximately 10%. Our modeling indicates that the laser will be able to meet its performance goals.

We report on the generation of tunable, ultrashort THz radiation between 2.0 and 5.3 THz by optical rectification of femtosecond laser pulse trains in the highly nonlinear crystal 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). Femtosecond pulse trains with a THz repetition rate are successfully synthesized from a single laser pulse using a zone plate which consists of a stack of thin glass plates. Using four glass slides we could experimentally demonstrate a substantial narrowing of the spectral bandwidth of the THz radiation. The spectral characterization of the THz pulses is accomplished using a Michelson interferometer. By simply tilting the zone plate the peak frequency is tuned from 2.0 to 5.3 THz. Even though higher and lower frequencies can be generated, the reported range is limited by the spectral characteristics of our detector. To our knowledge, our work demonstrates the first application of a zone plate for the generation of ultrashort THz pulses, tunable over a very large spectral range.

A multi-pulsed ruby laser system has been developed utilizing repetitive Q-switching technology. The laser system has applications in fields where high speed dynamic events are studied, e.g., ballistics and non-destructive test evaluation, using laser imaging diagnostics such as photography, holography, and various interferometric techniques. The laser system is capable of producing more than 50 pulses at a repetition rate in excess of 500 kHz with a nearly constant pulse-to-pulse energy of several mJ. The individual laser pulses are approximately 50 ns FWHM and the envelope of multiple pulses is greater than 200 microseconds. The method for multiple Q-switching by modulating the Pockels cell's quarter wave voltage and the formation of an individual Q- switched pulse have been investigated and a computational model has been formulated. The energy within the individual pulses formed in the oscillator cavity has been successfully increased without degradation of the temporal or pulse-to- pulse amplitude stability by propagating through an amplification section. Data of an amplified pulse train at a repetition rate of 500 kHz is given. Etalons for longitudinal mode selection and an iris for spatial mode selection have been incorporated for increased coherence and an image of a reconstructed hologram is presented.

Up to 0.75 Watt of blue laser light have been generated by second harmonic generation and additional sum frequency mixing of a 1.3 micrometer actively cw-modelocked Nd:YAG laser oscillator. Special attention has been paid to the design of the fundamental mode resonators, delivering output powers of up to 8 W at the fundamental wavelength with nearly diffraction limited beam quality. To overcome the thermally induced depolarizing birefringence a compensation scheme has been applied for further enhancement of the laser power.

The model LT-4Z electro-optical Q-switched flashlamp-pumped Nd:YAG laser is designed for hydrospheric studies. The laser generates a pulse of light in the blue-green region of the visible spectrum (532 nm), where the absorption of sea water is minimized, at pulse repetition rate of 100 - 500 Hz. This model is especially optimized for operation in airborne hydrography system. In this paper we describe the performance of a laser for complex airborne system which requires the conflicting specifications of high efficiency, small size, short pulsewidth, and high average power.

Theoretical and experimental results are presented to show that the etaloning problem in wavelength modulation experiments can be overcome by using harmonic detection that is greater than the commonly used second. The conditions under which such an advantage is obtained are discussed. Since the fringes due to parasitic Fabry-Perot etalons often place a limit to the ultimate sensitivity of such experiments, the method discussed has applications wherever sensitivity has to be increased. The method of higher harmonic detection is an alternative to synchronous mechanical jittering of an offending optical element that has been used in the past to average out the fringes.

Recent test results demonstrate the differences between laser cutting of Ti with different pulsed formats at 1.06 micrometer wavelength. The precision Laser Machining (PLM) consortium is dedicated to investigating improved processing obtained with the use of diode-pumped Nd:YAG lasers having high beam quality and high average power. One of the PLM lasers developed at TRW was used to determine the best parameters for laser cutting 0.034' Ti. Average power was available up to 340 W. Pulse repetition rates were 322 Hz with pulse lengths of 454 microseconds, while the modulated laser output had a 142 kHz micropulse train within the pulse envelope. Beam quality was sufficient to permit a 100 micrometer spot size to be used with f/10 focusing. Ar assist gas was used. At each setting of the laser average power the cutting tests usually were tried at 11 different speeds, up to 3'/second. The highest speed for which cutting is possible at a given average power is the threshold speed for that power. The cut specimens were evaluated for dross for a variety of rear surface Ar cross flow conditions. Each cut specimen also was evaluated for excess heating indicated by metallurgical and/or surface chemistry changes. Cutting at speeds above a critical minimum speed for each setting of laser average power greatly reduces degradation due to excess heating. Good cutting is possible between the threshold speed and this minimum speed (both a function of average power). Data for threshold and minimum speed were obtained for the pulsed and the modulated pulsed laser output. These tests also determined evidence of optimum conditions for cutting with a rear cross flow of Ar that substantially eliminates rear surface dross on the edge of the kerf. The quality of the cut edge was evaluated by inspection of its polished cross-section.

In this paper the results of the systematical investigation of the basic effects in Nd-doped silica fibers and their application in high-power fiber-lasers will be presented. The development and manufacturing of rare-earth doped double-clad optical fibers based on silica was done at the department 'Moderne Optik' of the Institut fur Physikalische Hochtechnologie e.V. Jena (IPHT). In the last few years at the IPHT Jena rare-earth doped double-clad fibers based on silica for the application in high-power fiber-lasers were developed and characterized. The doping with Neodymium as the laseractive component was one of the most important questions which were investigated. Many samples had to be made for the determination of the optimum concentration of Nd, the optimum codoping and geometry, respectively. As a result we realized a double-clad fiber with D-shape geometry of the pump-core. This D-shape resulted from ray-tracing calculations performed at the Laserzentrum Hannover e.V. (LZH) as an optimal solution for the high conversion efficiency of the pump power. Considering these numerical results, such double-clad fibers with different diameters of the Nd-doped laser-core (multimode or single-mode) was realized at IPHT by drawing of sidepolished preforms with different compositions and geometries by preserving the cross section of the preform. In a tight cooperation with the LZH cw-output powers of more than 30 W (multimode fiber-laser) and approx. 14 W (single-mode fiber-laser), respectively, were realized in the lab. First compact and transportable 19'-devices of high-power fiber- laser with a pumping power of approx. 10 W and an output power of more than two watts were developed and realized.

Different schemes were investigated to reduce the power threshold of phase conjugating mirrors based on stimulated Brillouin scattering (SBS). Two methods will be discussed in detail: A phase conjugating SBS-mirror based on multimode glass fibers and an SBS-based beam clean up arrangement. With a fiber phase conjugator we have investigated a continuously pumped Q-switched MOPA-system with SBS phase conjugation. The used fibers were characterized with respect to their reflectivity and power threshold at different repetition rates up to 20 kHz. Typical power thresholds are in the range of 200 W. The master oscillator consists of a ring resonator with an acousto-optical modulator to realize the Q-switch and a high coherence length of six meters. The beam is amplified in a double pass scheme with the fiber phase conjugator after the first pass to compensate phase distortions introduced by the amplifier. To remain the system relatively simple Nd:YALO was used as active medium to avoid depolarization effects. The beam clean up arrangement improves the beam quality outside the laser system. It is based on two wave mixing in an SBS- medium. An oscillator amplifier system was realized with such a beam clean up system based on carbon disulfide.

Laser diode pumped zigzag slab Nd:YAG MOPA (Master Oscillator Power Amplifier) system featuring high pulse energy and high average power has been developed for the pumping of ultra- short pulse laser system. The MOPA system consists of an oscillator, a preamplifier, two postamplifiers and image relay telescopes. The post amplifiers has an angle multiplexed ring type double-pass configuration. A pulse energy of 1.26 J and an average power of 251 W are obtained at the repetition rate of 200 Hz. The frequency doubled power using a LBO (LiB₃O₅) crystal is 105 W at the repetition rate of 170 Hz. The intensity profiles of the fundamental and the second harmonic are near top hat and is suitable for the pumping. In a preliminary experiment, effectiveness of the MOPA as a pump source of all solid state chirped pulse amplifier (CPA) system is demonstrated.

We developed a technique to compensate the wavefront distortion of ultra-short pulse Chirped Pulse Amplification (CPA) laser by applying a closed loop wavefront control system consisting of a Shack-Hartmann type wavefront sensor and Bimorph type deformable mirror. As a result of the experiments both Root Mean Square (RMS) and Peak to Valley (P-V) value of the wavefront distortion were reduced to less than 1/5 of the original value, and it was shown that the brightness of laser beam was improved by about five times.

Characteristics of a flashlamp pumped Ti:sapphire laser seeded by an external cavity laser diode (ECLD) is reported. The ECLD consists of a commercially available laser diode, a diffraction grating and a tuning mirror. The laser diode does not have an anti-reflection coating. The tuning mirror is used to feed the first order diffraction beam back to the laser diode. The ECLD has the property of mode-hopping suppression that is useful for the laser radar applications. The linewidth (FWHM) of the ECLD is about 0.3 pm with an output power of 6 mW and the wavelength tuning range is 11 nm from 769 nm to 780 nm. Injection into the cavity of the Ti:sapphire laser is made through a polarizing prism located between a Ti:sapphire rod and a pockels cell. The linewidth (FWHM) of the flashlamp pumped Ti:sapphire laser injection seeded by the ECLD was about 0.55 pm consequently. This laser system is applied to observe the potassium layer in the mesopause region.

A high energy flashlamp pumped Ti:sapphire laser has been developed for the pumping source of Yb:glass chirped pulse amplification. The free running oscillator generates 12 Joule/pulse at 793 nm at 1 Hz repetition. The output energy of 6 Joule/pulse at 920 nm has been obtained.

In single crystals of AgCl, BaCl₂, PbCl₂, SrCl₂, KPb₂Cl₅ with an unextended phonon spectrum (E less than 200 cm^-1), doped by Dy, the luminescence spectrum was found to cover a wide range from visible region to IR (4.3 mkm for KPb₂Cl₅), including well pronounced 1.31 mkm band, which is important for using in telecommunication amplifiers. The Rare Earth impurity was shown to enter the host matrice as RE³⁺ in chlorides, the only type of impurity centers being formed in the case of rhombic MeCl₂ crystals with Me equals Ba, P, S.

A simple quality model of stimulated Brillouin scattering of focused beams is suggested which allows us to quite accurately describe the shape of a Stocks pulse. For a case of totally overlapping pulses we have theoretically and experimentally investigated peculiarities of laser pulse deformations under amplification in two-pass and four-pass amplifiers with a phase-conjugate mirror when pump and spontaneous emission are neglected. Approximate formulas for determination of output pulse duration and duration of the pulse leading front are obtained. Parameters permitting to more effectively control the output pulse shape are found. We also suggest some ways to change the duration of a laser pulse without any significant change in its energy.

We present results of theoretical and experimental investigations of frequency sweeping mechanisms of the narrowline diode-pumped monolithic ring Nd:YAG laser radiation in multipass pulsed slab amplifier. The obtained value of the maximal chirp in the four-pass slab amplifier does not exceed 7.7 kHz when energy of the pump pulses is 36 J and the duration of these pulses is 0.3 ms.

We present results of precise measurement of spatial coherence degree and depolarization degree of the single frequency diode-pumped monolithic ring Nd:YAG laser radiation. An analysis is made of the factors influencing the spatial coherence and depolarization of miniature lasers with longitudinal diode pumping.

An experimental airborne laser fish finder has been developed and field trial has been conducted. The Q-switched and frequency-doubled Nd:YAG laser output is of 100 HZ pulse repetition rate, 2 MW peak power, 8 ns pulse width. The green light receiving telescope is transmissive with 1400 mm focal length and 200 mm aperture. The varying-gain control of PMT and logarithmic amplifier are used to compress the 10⁵ dynamic range of received signals. The main features of data real-time processing subsystem are of 200 Ms/s sampling rate, 8 bit resolution, adjacent average treatment of return waveforms with high noise, and pseudo-color display of water depth.

Dye doped polymeric solid samples of prismatic form and high optical quality were pumped by a short-pulse nitrogen laser. No external resonator or dispersive intracavity elements were added. For rather critical pumping conditions the usual narrow band laser spectrum bifurcates to a bichromatic one. A simple model of rate equations accounts for the main experimental results.

A polymeric high gain scattering medium based on IR-26 laser dye mixed with sub-micron alumina scatterers is described. Optical pumping at 1.06 micrometer with a Q-switched Nd:YAG laser results in isotropic, narrowband emission peaking at 1.18 micrometer. Alternative high gain, narrowband visible stimulated emitters utilizing a high density of microprism retroreflectors for optical feedback are also described. Optical pumping at 532 nm with the Q-switched output of a frequency-doubled Nd:YAG laser results in narrow linewidth, Stokes-shifted laser emission near 600 nm.

The performance of collinear and noncollinear pulsed barium borate optical parametric oscillators is analyzed under third harmonic Nd:YAG pumping. In the collinear case the effects of output coupling, cavity length and pump spotsize on threshold and slope efficiency have been measured and compared to a simple model. Tuning ranges, bandwidths and efficiencies are compared for collinear operation and for both directions of noncollinear operation. For a low pump divergence collinear operation is more efficient, but noncollinear operation is favored for a pump divergence in excess of 4 milliradians. Single frequency OPO operation with less than 250 MHz bandwidth is obtained using a simple new injection seeding technique for both signal and idler. Precise crystal temperature control is used to simultaneously manipulate the gain envelope and mode frequencies, ensuring stable seeding on the strongest mode.

An investigation of the influence of pump and laser excited state absorption (ESA), parasitic losses and pump parameters on Cr:YAG laser action has been carried out. A simple rate equation model has been extended to include ESA and dynamic pump effects. Results are compared with those obtained using a full spatio-temporal gain-switching model, and with experimental measurements in three temporal regimes. Comparison allows values for quantum efficiency and laser absorption, emission and ESA cross-sections to be allocated within the wide range of previously published data. Remaining discrepancies are attributed to thermal loading. An optimum pump energy is determined for a given fluence, and effective Cr:YAG energy scaling is demonstrated with only a slight threshold increase. Further enhancement is obtained using 500 ns pump pulses.

Generation of ultrashort pulses (picosecond range duration) in pyrromethene-580 (PM-580) and xanthene 11B dyes doped modified PMMA polymer lasers is reported. Active polymer elements were pumped by second harmonic radiation of the 50 picosecond Nd:YAG laser. A single-pulse and train-pulse laser generation was observed at different conditions (variable optical resonator length and pump energy) with a pulsewidth ranging from 140 ps to 30 ps. The train-pulse generation is attributed to mode-locking of a laser resonator. The lifetime (tau) _e, of an excited quantum state of a laser transition of the PM- 580 dye molecules has been estimated ((tau) _e equals 200 divided by 250 ps) from the pulse-train duration.